Innovations in the miniaturation of both every-day-use electronic devices and specialized micro-electromechanical devices has led to the need for an efficient power supply in smaller scale. In addition, on-demand power supplies in various environments which benefit from delayed activation have become an area of attention with the increased exploration of space, underwater and remote locations. Further, optimizing the power to size ratio has become a goal for the power source development in all electronic devices from the very large to micro-electric mechanical (MEMS) devices. Not only does the increase in existing technology (cell phones, lap-top computers, etc.) demand small portable energy supplies, but also the development of real portable instrumentation such as sensors, biomedical diagnosis and operational devices, accentuates the need for scaling down the size of batteries or enhancing the operational efficiency of batteries to enhance their functional range.
Existing large and small power energy sources vary widely in design and principles of operation. Fuel cells, piezoelectric and thermal-to-electric conversion mechanisms, turbines, and chemical batteries are some of the power systems currently under study for a wide variety of applications. Within the framework of existing technology, galvanic electrochemical cells represent a readily fabricated, simple concept that does not require movable parts when operating and can be fabricated in any desired size.
One particular desirable feature in the galvanic power source is the ability to supply power on demand when it is needed, thus necessitating an actuation mechanism. This mechanism serves to both supply power when it is needed only but also enhances battery life by providing a means for preservation of the reactants within the power cell until such time as their consumption is actually required. In addition, with a precise actuation mechanism, the amount of power supplied may be regulated as well as the length of life of the system may be extended.
Various systems for effecting actuation have been developed over the years. One such mechanism is described in Kao, U.S. Pat. No. 5,527,636. In the Kao device, an actuation block of absorbent material fed from a reservoir of electrolyte by a filament which contacts the electrodes when power is desired. In order for control to be maintained in the system, the Kao device requires moving parts in the mechanical movement of the absorbent pads be made which requires moving parts which are impractical in many applications.
Another system that works from moving parts is described in U.S. Pat. No. 5,536,592 to Celeste et al. Here the actual anode and/or cathode are mechanically contacted with the electolyte reservoir. The resultant control determined is by the rate at which the supply of electrode material is made available in the reservoir. Again, with mechanical moving parts required, the overall use of such a system is limited.
U.S. Pat. No. 6,403,244 to Faris et al is another example of a mechanical movable cathode type of cell with a system of sophisticated rollers advancing the cathode tape material through the system. Again, this structure is too complicated for many uses.
Another electrolye introduction means is described in Stone et al, U.S. Pat. No. 5,415,949. Here a sophisticated pump and control system circulate the electrolyte through the device. Included also are means for maintaining the integrity of the fluid itself as well as the by products of the chemical reaction which become recirculated in this system. Again, because of the complexity of this device, it is not suited for many applications.
A second Stone et al device disclosed in U.S. Pat. No. 5,567,540 also describes a pump structure with a solenoid valve to assist in the actuation. This valve, however, does not overcome the need for a simpler, less mechanically complicated system for delivery of the electrolyte to the reaction chamber.
The use of heat in the activation of the chemical reaction in fuel cells is also known in the art. One such example is Rock et al, U.S. Pat. No. 6,358,638. Here the membrane electrode assembly is preheated to enhance the start-up of the cells themselves. This is accomplished by a side exothermic reaction which has no effect on either the electrolyte system or the functioning of the cell after initial activation.
Wilson, U.S. Pat. No. 6,203,939, also discloses the use of heat in the operation of his battery system, however, this is related to a flux that is heated and then used to fuse to the electrodes to change their electrical properties.
U.S. Pat. No. 5,770,329 to Harney describes a heat-activated system in which the electrolyte is contained in a wafer which is heated to a molten state to activate the battery. Because of its location already being juxtaposed between the anode and cathode, this reference does not teach the use of a flow rate of the electolyte into the reaction chamber.
Finally, Weber, U.S. Pat. No. 4,650,732, discloses the use of heat for transfer of the electrolyte system from a remote reservoir to the cell. Here, the electrolyte is raised to a temperature sufficient for its use within the battery itself. With the increase in temperature, the electrolyte is able to flow at a more desired rate from its reservoir to the reaction chamber, but there is no disclosure that any elevated pressure is propelling that fluid in that flow path in a regulated fashion.